In a conventional brushless DC motor, three or more position detecting elements are required to switch current paths to a three phase coil.
FIG. 1 shows an example of the construction of a conventional brushless DC motor. The rotating position of a rotor 1 composed of a permanent magnet is detected by hall elements 2a, 2b and 2c. The electrical states of first driving transistors 4a, 4b, 4c and second driving transistors 5a, 5b, 5c are switched and controlled by a processing circuit 3 corresponding to the rotor detecting signals, and the current paths to the three phase coils 6a, 6b, 6c are switched. As mentioned above, in the case that hall elements 2a, 2b, 2c are used as the position detecting elements, the number of parts of the motor increases, and there is a disadvantage that the circuit is complicated. Moreover, in the case that such a brushless DC motor is used as a motor for a compressor, the hall elements are used in a high temperature and a high voltage state because a large amount of current flows, and therefore, reliability or life time is seriously diminished.